There has previously been developed a type of electronic musical instrument in which a tone-source-signal pulse generator, a plurality of order pulse generators and a plurality of musical-tone-waveform forming circuits are connected in order. The plurality of order pulse generators each comprises an address counter, which is composed of a plurality of frequency-dividers, each having a frequency-dividing ratio of two, connected in series with one another so that a number of frequency-divided pulses are generated at output terminals of those dividers. Each order pulse generator also includes a matrix circuit which serves to decode those frequency-divided pulses to take out in order from its respective output terminals pulses l to n.
The musical-tone-waveform forming circuits each comprises a musical-tone-waveform memory circuit which has a sampling number (set values previously memorized are read and are converted into digital signals constituting output signals) corresponding to the above-mentioned order pulses l to n, and a D-A converter which serves to convert those digital signals obtained in order by the order pulses into an analog signal for forming a musical-tone waveform.
Thus, if the pulse oscillation frequency of the tone-source-signal pulse generator in the known arrangement is f, the output signal thereof is constituted by a series of pulses which are decoded by the order pulse generators to generate repeatedly the order pulses l to n which are applied as an input to each musical-tone-waveform forming circuit, whereby each signal musical-tone waveform is formed by the order pulses from l to n, and thus there can be obtained a musical-tone signal of the frequency f/n as a whole. The above has been already disclosed in U.S. Pat. No. 3,515,792.
With this known arrangement, in order to obtain musical-tone signals extending over a wide octave range, the oscillation frequency of the tone-source-signal pulse generator must be as high as 2.00024 MHz, for instance, and the number n of the order pulses in each of the order pulse generators must be made, respectively, 239, 253 . . . 451, 478 . . . .
The fact that the number n is so varied as indicated above results in defects such that the sampling number of the musical-tone-waveform memory circuit in each of the musical-tone-waveform forming circuits is not only differentiated from one another but also is considerably large in number. Thus the manufacturing and setting thereof becomes troublesome.
If it is now established that the sampling number of the musical-tone-waveform memory circuit is 32, the number of order pulses also becomes 32, and one cycle of musical-tone waveform is formed by thirty-two input pulses. This is equal to the result that the frequency-dividing ratio is 32. If, then, it is assumed that the sampling number is 32 and the finally required frequency-dividing ratio is 239, it will be clearly appreciated that, in the case where a pulse counter of a frequency-dividing ratio of 7.46 is provided between the order pulse generator and the tone-source signal-pulse generator, the whole frequency-dividing ratio becomes 239 and thereby the correct frequency for the musical-tone signal can be obtained. However, a pulse counter with such a frequency-dividing ratio can not be readily made. If, therefore, the frequency-dividing ratio thereof is conveniently fixed to be 8, the whole frequency-dividing ratio becomes 8 .times. 32 = 256, and thus there is caused such an inconvenience that the resultant signal becomes 7813.43 Hz in frequency, whereas the correct frequency thereof should be 8360.21 Hz. There is a large error therebetween and the resultant musical tone is not fit for hearing.